Using Destination with StringSliceFlags break DisableSliceFlagSeparator and SliceFlagSeperator controls

[dereknola]

My urfave/cli version is

v2.27.5

Checklist

• Are you running the latest v2 release? The list of releases is here.
• Did you check the manual for your release? The v2 manual is here
• Did you perform a search about this problem? Here's the GitHub guide about searching.

Dependency Management

• My project is using go modules.

Describe the bug

I've tracked this down to how the flags are defined. Specifically, if a StringSliceFlag is given a Destination to store the StringSlice, the settings for flag seperators are not carried over when processing this Slice.

To reproduce

I've created a simple golang program to replicate this issue.

CODE

package main

import (
	"fmt"
	"os"

	"github.com/urfave/cli/v2"
)

var aaStorage cli.StringSlice

func main() {
	app := &cli.App{
		DisableSliceFlagSeparator: true,
		Commands: []*cli.Command{
			{
				Name: "runner",
				Flags: []cli.Flag{
					&cli.StringSliceFlag{
						Name:        "aa",
						Usage:       "Multi string with Destination",
						Destination: &aaStorage,
					},
					&cli.StringSliceFlag{
						Name:  "bb",
						Usage: "Multi string default",
					},
				},
				Action: func(c *cli.Context) error {
					fmt.Println("aa raw:", aaStorage)
					fmt.Println("aa value:", aaStorage.Value())
					bbStorage := c.StringSlice("bb")
					fmt.Println("bb raw:", bbStorage)
					return nil
				},
			},
		},
	}

	err := app.Run(os.Args)
	if err != nil {
		fmt.Println(err)
	}
}

Describe the steps or code required to reproduce the behavior

Observed behavior

Running above code with

./main runner --aa="11,22" --aa="33" --bb="44,55" --bb="66"

Produces

aa raw: {[11 22 33] { false false} true false}
aa value: [11 22 33]
bb raw: [44,55 66]

What did you see happen immediately after the reproduction steps
above?

Expected behavior

DisableSliceFlagSeparator is respected on all Destination values

Additional context

I work on k3s and we are attempting to migrate from v1 to v2. During this process, we have had difficulty with the changes around StringSliceFlag. Specifically issues with using the DisableSliceFlagSeparator option, as we pass flag values that contain , into embedded collectables.
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link a failing build here.

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